2 * Copyright 2014 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
19 #include <glog/logging.h>
20 #include <folly/io/async/AsyncTimeout.h>
21 #include <folly/io/async/TimeoutManager.h>
22 #include <folly/wangle/Executor.h>
30 #include <boost/intrusive/list.hpp>
31 #include <boost/utility.hpp>
33 #include <event.h> // libevent
40 typedef std::function<void()> Cob;
41 template <typename MessageT>
42 class NotificationQueue;
44 class EventBaseObserver {
46 virtual ~EventBaseObserver() {}
48 virtual uint32_t getSampleRate() const = 0;
50 virtual void loopSample(
51 int64_t busyTime, int64_t idleTime) = 0;
55 * This class is a wrapper for all asynchronous I/O processing functionality
57 * EventBase provides a main loop that notifies EventHandler callback objects
58 * when I/O is ready on a file descriptor, and notifies AsyncTimeout objects
59 * when a specified timeout has expired. More complex, higher-level callback
60 * mechanisms can then be built on top of EventHandler and AsyncTimeout.
62 * A EventBase object can only drive an event loop for a single thread. To
63 * take advantage of multiple CPU cores, most asynchronous I/O servers have one
64 * thread per CPU, and use a separate EventBase for each thread.
66 * In general, most EventBase methods may only be called from the thread
67 * running the EventBase's loop. There are a few exceptions to this rule, for
68 * methods that are explicitly intended to allow communication with a
69 * EventBase from other threads. When it is safe to call a method from
70 * another thread it is explicitly listed in the method comments.
73 private boost::noncopyable, public TimeoutManager, public wangle::Executor
77 * A callback interface to use with runInLoop()
79 * Derive from this class if you need to delay some code execution until the
80 * next iteration of the event loop. This allows you to schedule code to be
81 * invoked from the top-level of the loop, after your immediate callers have
84 * If a LoopCallback object is destroyed while it is scheduled to be run in
85 * the next loop iteration, it will automatically be cancelled.
89 virtual ~LoopCallback() {}
91 virtual void runLoopCallback() noexcept = 0;
92 void cancelLoopCallback() {
96 bool isLoopCallbackScheduled() const {
97 return hook_.is_linked();
101 typedef boost::intrusive::list_member_hook<
102 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
106 typedef boost::intrusive::list<
108 boost::intrusive::member_hook<LoopCallback, ListHook,
109 &LoopCallback::hook_>,
110 boost::intrusive::constant_time_size<false> > List;
112 // EventBase needs access to LoopCallbackList (and therefore to hook_)
113 friend class EventBase;
114 std::shared_ptr<RequestContext> context_;
118 * Create a new EventBase object.
123 * Create a new EventBase object that will use the specified libevent
124 * event_base object to drive the event loop.
126 * The EventBase will take ownership of this event_base, and will call
127 * event_base_free(evb) when the EventBase is destroyed.
129 explicit EventBase(event_base* evb);
133 * Runs the event loop.
135 * loop() will loop waiting for I/O or timeouts and invoking EventHandler
136 * and AsyncTimeout callbacks as their events become ready. loop() will
137 * only return when there are no more events remaining to process, or after
138 * terminateLoopSoon() has been called.
140 * loop() may be called again to restart event processing after a previous
141 * call to loop() or loopForever() has returned.
143 * Returns true if the loop completed normally (if it processed all
144 * outstanding requests, or if terminateLoopSoon() was called). If an error
145 * occurs waiting for events, false will be returned.
150 * Wait for some events to become active, run them, then return.
152 * When EVLOOP_NONBLOCK is set in flags, the loop won't block if there
153 * are not any events to process.
155 * This is useful for callers that want to run the loop manually.
157 * Returns the same result as loop().
159 bool loopOnce(int flags = 0);
162 * Runs the event loop.
164 * loopForever() behaves like loop(), except that it keeps running even if
165 * when there are no more user-supplied EventHandlers or AsyncTimeouts
166 * registered. It will only return after terminateLoopSoon() has been
169 * This is useful for callers that want to wait for other threads to call
170 * runInEventBaseThread(), even when there are no other scheduled events.
172 * loopForever() may be called again to restart event processing after a
173 * previous call to loop() or loopForever() has returned.
175 * Throws a std::system_error if an error occurs.
180 * Causes the event loop to exit soon.
182 * This will cause an existing call to loop() or loopForever() to stop event
183 * processing and return, even if there are still events remaining to be
186 * It is safe to call terminateLoopSoon() from another thread to cause loop()
187 * to wake up and return in the EventBase loop thread. terminateLoopSoon()
188 * may also be called from the loop thread itself (for example, a
189 * EventHandler or AsyncTimeout callback may call terminateLoopSoon() to
190 * cause the loop to exit after the callback returns.) If the loop is not
191 * running, this will cause the next call to loop to terminate soon after
192 * starting. If a loop runs out of work (and so terminates on its own)
193 * concurrently with a call to terminateLoopSoon(), this may cause a race
196 * Note that the caller is responsible for ensuring that cleanup of all event
197 * callbacks occurs properly. Since terminateLoopSoon() causes the loop to
198 * exit even when there are pending events present, there may be remaining
199 * callbacks present waiting to be invoked. If the loop is later restarted
200 * pending events will continue to be processed normally, however if the
201 * EventBase is destroyed after calling terminateLoopSoon() it is the
202 * caller's responsibility to ensure that cleanup happens properly even if
203 * some outstanding events are never processed.
205 void terminateLoopSoon();
208 * Adds the given callback to a queue of things run after the current pass
209 * through the event loop completes. Note that if this callback calls
210 * runInLoop() the new callback won't be called until the main event loop
211 * has gone through a cycle.
213 * This method may only be called from the EventBase's thread. This
214 * essentially allows an event handler to schedule an additional callback to
215 * be invoked after it returns.
217 * Use runInEventBaseThread() to schedule functions from another thread.
219 * The thisIteration parameter makes this callback run in this loop
220 * iteration, instead of the next one, even if called from a
221 * runInLoop callback (normal io callbacks that call runInLoop will
222 * always run in this iteration). This was originally added to
223 * support detachEventBase, as a user callback may have called
224 * terminateLoopSoon(), but we want to make sure we detach. Also,
225 * detachEventBase almost always must be called from the base event
226 * loop to ensure the stack is unwound, since most users of
227 * EventBase are not thread safe.
229 * Ideally we would not need thisIteration, and instead just use
230 * runInLoop with loop() (instead of terminateLoopSoon).
232 void runInLoop(LoopCallback* callback, bool thisIteration = false);
235 * Convenience function to call runInLoop() with a std::function.
237 * This creates a LoopCallback object to wrap the std::function, and invoke
238 * the std::function when the loop callback fires. This is slightly more
239 * expensive than defining your own LoopCallback, but more convenient in
240 * areas that aren't performance sensitive where you just want to use
241 * std::bind. (std::bind is fairly slow on even by itself.)
243 * This method may only be called from the EventBase's thread. This
244 * essentially allows an event handler to schedule an additional callback to
245 * be invoked after it returns.
247 * Use runInEventBaseThread() to schedule functions from another thread.
249 void runInLoop(const Cob& c, bool thisIteration = false);
251 void runInLoop(Cob&& c, bool thisIteration = false);
254 * Adds the given callback to a queue of things run before destruction
255 * of current EventBase.
257 * This allows users of EventBase that run in it, but don't control it,
258 * to be notified before EventBase gets destructed.
260 * Note: will be called from the thread that invoked EventBase destructor,
261 * before the final run of loop callbacks.
263 void runOnDestruction(LoopCallback* callback);
265 void runBeforeLoop(LoopCallback* callback);
268 * Run the specified function in the EventBase's thread.
270 * This method is thread-safe, and may be called from another thread.
272 * If runInEventBaseThread() is called when the EventBase loop is not
273 * running, the function call will be delayed until the next time the loop is
276 * If runInEventBaseThread() returns true the function has successfully been
277 * scheduled to run in the loop thread. However, if the loop is terminated
278 * (and never later restarted) before it has a chance to run the requested
279 * function, the function may never be run at all. The caller is responsible
280 * for handling this situation correctly if they may terminate the loop with
281 * outstanding runInEventBaseThread() calls pending.
283 * If two calls to runInEventBaseThread() are made from the same thread, the
284 * functions will always be run in the order that they were scheduled.
285 * Ordering between functions scheduled from separate threads is not
288 * @param fn The function to run. The function must not throw any
290 * @param arg An argument to pass to the function.
292 * @return Returns true if the function was successfully scheduled, or false
293 * if there was an error scheduling the function.
296 bool runInEventBaseThread(void (*fn)(T*), T* arg) {
297 return runInEventBaseThread(reinterpret_cast<void (*)(void*)>(fn),
298 reinterpret_cast<void*>(arg));
301 bool runInEventBaseThread(void (*fn)(void*), void* arg);
304 * Run the specified function in the EventBase's thread
306 * This version of runInEventBaseThread() takes a std::function object.
307 * Note that this is less efficient than the version that takes a plain
308 * function pointer and void* argument, as it has to allocate memory to copy
309 * the std::function object.
311 * If the EventBase loop is terminated before it has a chance to run this
312 * function, the allocated memory will be leaked. The caller is responsible
313 * for ensuring that the EventBase loop is not terminated before this
316 * The function must not throw any exceptions.
318 bool runInEventBaseThread(const Cob& fn);
321 * Runs the given Cob at some time after the specified number of
322 * milliseconds. (No guarantees exactly when.)
324 * @return true iff the cob was successfully registered.
329 TimeoutManager::InternalEnum = TimeoutManager::InternalEnum::NORMAL);
332 * Set the maximum desired latency in us and provide a callback which will be
333 * called when that latency is exceeded.
335 void setMaxLatency(int64_t maxLatency, const Cob& maxLatencyCob) {
336 maxLatency_ = maxLatency;
337 maxLatencyCob_ = maxLatencyCob;
341 * Set smoothing coefficient for loop load average; # of milliseconds
342 * for exp(-1) (1/2.71828...) decay.
344 void setLoadAvgMsec(uint32_t ms);
347 * reset the load average to a desired value
349 void resetLoadAvg(double value = 0.0);
352 * Get the average loop time in microseconds (an exponentially-smoothed ave)
354 double getAvgLoopTime() const {
355 return avgLoopTime_.get();
359 * check if the event base loop is running.
361 bool isRunning() const {
362 return loopThread_.load(std::memory_order_relaxed) != 0;
366 * wait until the event loop starts (after starting the event loop thread).
368 void waitUntilRunning();
370 int getNotificationQueueSize() const;
372 void setMaxReadAtOnce(uint32_t maxAtOnce);
375 * Verify that current thread is the EventBase thread, if the EventBase is
378 bool isInEventBaseThread() const {
379 auto tid = loopThread_.load(std::memory_order_relaxed);
380 return tid == 0 || pthread_equal(tid, pthread_self());
383 bool inRunningEventBaseThread() const {
384 return pthread_equal(
385 loopThread_.load(std::memory_order_relaxed), pthread_self());
388 // --------- interface to underlying libevent base ------------
389 // Avoid using these functions if possible. These functions are not
390 // guaranteed to always be present if we ever provide alternative EventBase
391 // implementations that do not use libevent internally.
392 event_base* getLibeventBase() const { return evb_; }
393 static const char* getLibeventVersion();
394 static const char* getLibeventMethod();
397 * only EventHandler/AsyncTimeout subclasses and ourselves should
400 * This is used to mark the beginning of a new loop cycle by the
401 * first handler fired within that cycle.
404 bool bumpHandlingTime();
406 class SmoothLoopTime {
408 explicit SmoothLoopTime(uint64_t timeInterval)
409 : expCoeff_(-1.0/timeInterval)
411 , oldBusyLeftover_(0) {
412 VLOG(11) << "expCoeff_ " << expCoeff_ << " " << __PRETTY_FUNCTION__;
415 void setTimeInterval(uint64_t timeInterval);
416 void reset(double value = 0.0);
418 void addSample(int64_t idle, int64_t busy);
424 void dampen(double factor) {
431 int64_t oldBusyLeftover_;
435 const std::shared_ptr<EventBaseObserver>& observer) {
436 observer_ = observer;
439 const std::shared_ptr<EventBaseObserver>& getObserver() {
444 * Set the name of the thread that runs this event base.
446 void setName(const std::string& name);
449 * Returns the name of the thread that runs this event base.
451 const std::string& getName();
453 /// Implements the wangle::Executor interface
454 void add(Cob fn) override {
455 // runInEventBaseThread() takes a const&,
456 // so no point in doing std::move here.
457 runInEventBaseThread(fn);
463 void attachTimeoutManager(AsyncTimeout* obj,
464 TimeoutManager::InternalEnum internal);
466 void detachTimeoutManager(AsyncTimeout* obj);
468 bool scheduleTimeout(AsyncTimeout* obj, std::chrono::milliseconds timeout);
470 void cancelTimeout(AsyncTimeout* obj);
472 bool isInTimeoutManagerThread() {
473 return isInEventBaseThread();
476 // Helper class used to short circuit runInEventBaseThread
477 class RunInLoopCallback : public LoopCallback {
479 RunInLoopCallback(void (*fn)(void*), void* arg);
480 void runLoopCallback() noexcept;
488 * Helper function that tells us whether we have already handled
489 * some event/timeout/callback in this loop iteration.
491 bool nothingHandledYet();
493 // --------- libevent callbacks (not for client use) ------------
495 static void runFunctionPtr(std::function<void()>* fn);
497 // small object used as a callback arg with enough info to execute the
498 // appropriate client-provided Cob
499 class CobTimeout : public AsyncTimeout {
501 CobTimeout(EventBase* b, const Cob& c, TimeoutManager::InternalEnum in)
502 : AsyncTimeout(b, in), cob_(c) {}
504 virtual void timeoutExpired() noexcept;
510 typedef boost::intrusive::list_member_hook<
511 boost::intrusive::link_mode<boost::intrusive::auto_unlink> > ListHook;
515 typedef boost::intrusive::list<
517 boost::intrusive::member_hook<CobTimeout, ListHook, &CobTimeout::hook>,
518 boost::intrusive::constant_time_size<false> > List;
521 typedef LoopCallback::List LoopCallbackList;
522 class FunctionRunner;
524 bool loopBody(int flags = 0);
526 // executes any callbacks queued by runInLoop(); returns false if none found
527 bool runLoopCallbacks(bool setContext = true);
529 void initNotificationQueue();
531 CobTimeout::List pendingCobTimeouts_;
533 LoopCallbackList loopCallbacks_;
534 LoopCallbackList noWaitLoopCallbacks_;
535 LoopCallbackList onDestructionCallbacks_;
537 // This will be null most of the time, but point to currentCallbacks
538 // if we are in the middle of running loop callbacks, such that
539 // runInLoop(..., true) will always run in the current loop
541 LoopCallbackList* runOnceCallbacks_;
543 // stop_ is set by terminateLoopSoon() and is used by the main loop
544 // to determine if it should exit
547 // The ID of the thread running the main loop.
548 // 0 if loop is not running.
549 // Note: POSIX doesn't guarantee that 0 is an invalid pthread_t (or
550 // even that atomic<pthread_t> is valid), but that's how it is
551 // everywhere (at least on Linux, FreeBSD, and OSX).
552 std::atomic<pthread_t> loopThread_;
554 // pointer to underlying event_base class doing the heavy lifting
557 // A notification queue for runInEventBaseThread() to use
558 // to send function requests to the EventBase thread.
559 std::unique_ptr<NotificationQueue<std::pair<void (*)(void*), void*>>> queue_;
560 std::unique_ptr<FunctionRunner> fnRunner_;
562 // limit for latency in microseconds (0 disables)
565 // exponentially-smoothed average loop time for latency-limiting
566 SmoothLoopTime avgLoopTime_;
568 // smoothed loop time used to invoke latency callbacks; differs from
569 // avgLoopTime_ in that it's scaled down after triggering a callback
570 // to reduce spamminess
571 SmoothLoopTime maxLatencyLoopTime_;
573 // callback called when latency limit is exceeded
576 // we'll wait this long before running deferred callbacks if the event
578 static const int kDEFAULT_IDLE_WAIT_USEC = 20000; // 20ms
580 // Wrap-around loop counter to detect beginning of each loop
581 uint64_t nextLoopCnt_;
582 uint64_t latestLoopCnt_;
585 // Observer to export counters
586 std::shared_ptr<EventBaseObserver> observer_;
587 uint32_t observerSampleCount_;
589 // Name of the thread running this EventBase